Manufacture of tin alkyl compounds



United States Patent 3,028,320 Patented Apr. 3, 1962 Free 3,028,320 MANUFACTURE OF TIN ALKYL COMPOUNDS Paul Kohetz and Richard C. Pinkerton, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N.Y., a cor- 5 poration of Delaware No Drawing, Filed Feb. 1, 1960, Ser. No. 5,672 4 Claims. (Cl. 20459) This invention relates to the manufacture of tin ongano compounds and more particularly to the manufacture of tin tetraorgano compounds and especially tin tetraal-kyl compounds, such as tin tetraethyl.

Tin alkyl compounds are highly useful as intermediates in making stabilizers for polymeric materials, such as vinyl chloride or for stabilising components for liquid chlorinated hydrocarbon compounds such as are used in transformer dielectric liquids or the like. Heretofore, the accepted method for making tin alkyl compounds, such as tetrabutyl tin, has been the reaction of stannic chloride by the Grignard process, i.e., reacting the stannic chloride with butyl magnesium chloride to form tetrabutyl tin according to the following equation:

Sodium tin alloys have been proposed for manufacture of tetraalk-yl tins by reacting with lower alkyl chlorides, but this type of process is relatively inefiicient in that a preponderant proportion of the tin metal originally fed, as alloy, is released as elemental metal and must be recovered and recycled. Accordingly, a significant need has existed for an eifective and economical process for the production of tin hydrocarbon compounds.

It is accordingly an object of this invention to provide an improved process for the manufacture of tin tetraorgano compounds and especially tin alkyl compounds, such as tin tetraethyl. Another object is to provide an electrolytic process capable of producing substantial quantities of tin alkyl compounds in a relatively small electrolytic cell. Still another object is a process in which the tin alkyl products can be readily separated from the electrolyte and by-products by simple and economical techniques and in which the by-product can be regenerated and returned to the cell.

These and other objects of the invention are obtained if the electrolyte contains an alkali metal aluminum methyl compound and especially an alkali metal alumiq num tetraalkyl in which at least one of the alkyl groups is a methyl group. An especially desirable electrolyte for carrying out the process of this invention comprises a mixture or complex of an alkali metal aluminum methyl compound with an alkali metal aluminum tetraalkyl or tetraaryl, the organo groups of the latter compound containing from 2 to about 12 carbon atoms.

More specifically the process for manufacture of the tin alkyl compounds in accordance with this invention comprises passing an electrolyzing current from a tin anode through an electrolyte comprising an alkali metal aluminum tetraorgano compound having the formula wherein M is an alkali metal, R is selected from the group consisting of alkyl and aryl groups, each group containing from 2 to 12 carbon atoms, and x is an integer of from 1 to 4 inclusive. An especially preferred embodiment of this invention relates to the manufacture of tin alkyl products using a mixed complex having, in addition to the alkali metal aluminum methyl compound, another alkali metal aluminum compound in which all of the organo groups contain from 2 to 12 carbon atoms. A11 especially preferred electrolyte contains more than one alkali metal, e.g. both sodium and potassium or sodium and lithium or all three metals.

The electrolyte mixture usually contains from 5-95 percent of the alkali metal aluminum methyl compound. Best results are obtained using a concentration of the alkali metal aluminum methyl compound of from 10-75 mole percent. A preferred concentration of the alkali metal aluminum methyl compound in the electrolyte mixture is from about 20-65 mole percent. In general, the electrolyte mixture should have a melting point below about 150 C. for manufacture of alkyl tin compounds and the most preferred electrolytes have melting points below about C. The pure sodium aluminum tetramethyl, for example, has a melting point in excess of 240 C. but the addition of relatively small quantities of the sodium or potassium aluminum tetraethyl, or higher organo compounds, sharply reduces the melting point of the mixture.

The above process involves exceptionally simple techniques and apparatus and provides high yields of the tin alkyl compounds, in essence, directly from tin, hydrogen, and olefin. The tin metal is converted at the anode to tin organo compounds and the electrolyte, in the manufacture of such products, can be regenerated, either periodically or continuously, by reaction with an olefin and hydrogen. The process is capable of extremely high production capacities because it can be operated at high current densities, and this is practical because of the very high conductivity of the complex electrolyte. The process can be conducted at these high current densities at temperatures well below the thermal decomposition temperature of the tin alkyl products. This good conductivity also materially reduces the problem of heat removal from the cell. A particularly surprising feature of this invention is that the tin alkyl products contain only minor proportions of methyl groups when the electrolyte contains R groups in addition to the methyl groups, but instead the methyl groups are recovered as aluminum-containing compounds which can be readily converted to the complex alkali metal aluminum methyl compound and recycled to the electrolytic cell. The aluminum-methyl by-prouct (without alkali metal) has a materially lower boiling point than the tin alkyl compound and thus can be readily separated from the tin organo product. Essential functions of the alkali metal aluminum methyl compound, in other words, are to provide high conductivity to the system and at the same time form an aluminum-containing by-product which can be readily separated from the tin organo product. As will be seen from the following discussion, through regeneration of the alkali metal aluminum alkyl, the only raw materials necessary for this process are metallic tin, olefin and hydrogen. When using the mixed electrolyte, the aluminum methyl compound is formed in from 5-30 percent of the total product and in some cases up to about 50 percent and can be recovered as a second product or converted back to the alkali metal-containing compound for reuse in the process.

The reaction of the present process can be illustrated, using the mixed electroltye, as follows:

MAlMei wherein M, Me, and R are as defined above. The aluminum trialkyl can be separated from the tin tetraorgano compound by distillation or by chemical means. In addition, some methyl-containing aluminum compounds are formed which may, under certain conditions, react with the AlR to form mixed organo compounds. A suitable chemical method of recovering the tin organo products and regenerating the aluminum compound is to react the aluminum compound with an alkali metal boron compound in accordance with the following equation:

A1R3 BRa The complex can then be regenerated by the following equations:

As discussed above, it is convenient to carry out the electrolysis of this invention using an electrolyte containing both an alkali metal aluminum tetramethyl and an alkali metal aluminum tetraalkyl in which the alkyl contains at least 2 carbon atoms. It is to be recognized that the electrolyte can contain two or more methyl-containing compounds, such as sodium aluminum methyl triethyl, sodium aluminum dimethyl diethyl and sodium aluminum trimethylethyl, and especially mixed compounds of two or more alkali metals.

The present process can be carried out over an exceedingly Wide temperature range, generally from to about 200 C. The upper temperature at the anode is sometimes limited by the decomposition temperature of the tin tetraorgano product. Accordingly, with tin tetraethyl as a predominant product component, it is usually desirable to maintain the temperature below about 100 to 110 C.

In some cases it is desirable to use a solvent for the tin organo compound, directly in the electrolysis cell. Such solvents can be either miscible or non-miscible with the electrolyte. Typical examples of suitable extractants are aliphatic and aromatic hydrocarbon liquids. Excellent results are obtained with such extractants as kerosene and mineral oil used in a concentration of from about 25 to 75 percent of the tin tetraorgano product formed.

Normally, the electrolysis is conducted at or near atmospheric pressure. However, a pressure of inert gas such as nitrogen can be employed when desired, especially to assure an oxygen and moisture-free system. In some cases, it is desirable to employ a reduced pressure to effect distillation of the tin organo compound and/or the aluminum compound from the cell during the electrolysis.

The following are typical examples of the process of this invention, all parts being given in parts by weight.

Example I A closed cell was provided with an annular copper cathode and an axially positioned tin anode. To this cell was added an electrolyte containing equimo-lar proportions of sodium aluminum tetramethyl and sodium alumisodium boron tetraethyl at a temperature of 100 C. to produce the corresponding sodium aluminum alkyls and the corresponding alkyl boron compounds. The latter are gases at reaction temperature and can be readily separated from the mixture. The sodium aluminum tetraalkyl complex is readily separated from the tin alkyl products by filtration and can thereafter be recycled to the electrolytic cell.

The tin hydrocarbon product liquid from the foregoing example consistcd of predominant quantities of tin tetraethyl, with minor quantities of tin alkyl compounds having appreciable methyl radicals therein and an even smaller proportion of tin alkyl compounds of ditin types, e.g. hexaethyl ditin.

Example 11 Example I is repeated except that the electrolyte consisted of 3 moles of sodium aluminum tetraethyl and 1 mole of sodium aluminum tetrarnethyl. Comparable anode efficiency and current density are experienced.

Example IV Example III is repeated except that 10 mole percent potassium is added to displace a corresponding quantity of sodium, providing an electrolyte containing both soium and potassium. In this instance, a higher anode efliciency is achieved at a comparable current density.

The following tabulated examples are carried out in a similar fashion to Example I. The product in each instance is a tin alkylproduct liquid, predominating in the tetraalkyl corresponding to the longer alkyl group present in the electrolyte mixture. In addition to the principal 4O component of the product, minor components present include the dialkyl tin compounds and some small proportion of di-tin compounds, illustrated by hexaethyl distannane. The alkyl groups in the tin organometallic products are predominantly the higher alkyl groups, but a small proportion of methyl radicals occur, of from 5 to 25 percent of the total alkyl rgoups. In Example VIII, however, all the alkyl groups in the product are methyl radicals.

Solvent or Extractant MAlMe4/ Temper- Example MAlMe; MAlR MAIR; Proportionature, Product-major N 0. mole based on tin- 0. component ratio Type organo product, percent KAlM KAl(i-pr)t 8 160 Tin tetraisopropyl. NaAlMe NaAl(OsH 0. 1 180 Tin tetraphenyl. LiAlMe; N aAl(CsH1 0. 3 40 Tin tetraoctyl. RbA1Me NaAl(OH3)4. 5 100 The tetramethyl. NaAlMel- CsAlEt 2 125 Tin tetraethyl.

i-pr=isopropyl.

CsH =phenyL num tetraethyl. The cell was heated to a temperature of approximately 100 C. and a 3.8 volt potential was applied across the electrodes. The current density in amperes/sq. cm. Was 0.25. The anode efiiciency was approximately 80 percent. Tin alkyl compounds were produced at the anode and formed a separate phase from the electrolyte. The product was drained by gravity from the cell. Sodium metal was deposited at the cathode during the electrolysis and this was also removed as a liquid from the cell. The methyl and ethyl aluminum byproducts, mixed with the tin alkyl product compounds Example X Example I is repeated except that the electrolyte consists of sodium aluminum tetrarnethyl, potassium aluminum tetraethyl, and lithium aluminum tetraethyl in equimolecular proportions. In addition, mineral oil (80 Weight percent of the tin alkyl product) is employed in the electrolyte as an extractant to aid in the removal of the tin alkyl product.

The alkali metal aluminum methyl compounds can be prepared in one of several ways. A convenient process involves the displacement reaction of the elemental alkali andminm q m s of electrolyte, are then reacted with metal with aluminum trimethyl forming the correspond ing alkali metal tetramcthyl. These compounds can also be prepared by the addition reaction of aluminum trimethyl and alkali metal alkyl compounds, or contrariwise, aluminum trialkyls with sodium methyl. A particularly suitable method for the mixed alkyl compounds is the reaction of an olefin, e.g. ethylene with an alkali metal aluminum alkyl hydride. Likewise, the complex methyl compound can be made by reaction of an alkyl halide with an alkali metal and trimethyl aluminum.

The alkali metal aluminum tetraorgano compound (the organo group containing 2 or more carbon atoms) can be made by analogous processes. That is, the alkali metal can be reacted directly with the aluminum triorgano compound, e.g. sodium reacts with triethyl a1uminum to form sodium aluminum tetraethyl and metallic aluminum. Likewise, sodium ethyl and other alkali metal organo compounds will react directly with the aluminum triorgano compound to form the complex as an addition product. The corresponding organo halides will also react with the alkali metal and aluminum triorgano compound to form the complex, for example, sodium reacts with ethyl chloride and aluminum triethyl to form sodium aluminum tetraethyl. A particularly desirable method of preparing the alkyl complexes is the process discussed above with reference to regeneration of the trialkyl aluminum electrolyte. Trialkyl aluminums, e.g. trimethyl aluminum or triethyl aluminum, will react with an alkali metal hydride such as sodium hydride to form the corresponding complex hydride, e.g. sodium aluminum triethyl hydride, which can thereafter be reacted with a suitable olefin, as discussed above, forming sodium aluminum tetraethyl. All of the above preparation reactions can be carried out at temperatures from about C. to about 150 C.

Normally, solvents are not employed in the electrol ysis system of this invention since they tend to reduce the conductivity of the electrolyte. However, when they are desired for certain purposes, such as to provide a more fluid medium, it is best to employ hydrocarbons, especially aromatic hydrocarbons which are unreactive with the reactants, products and electrolyte. Particularly suitable solvents are toluene, the xylenes and other substituted benzene and naphthalene compounds. In some cases the ethers can be used, especially the glycol ethers, such as ethylene glycol dialkyl ethcrs, diethylene glycol dialkyl ethers and triethylene glycol dialkyl ethers, wherein the alkyl group contains from 1-6 carbon atoms.

We claim:

1. A process for the manufacture of tetraethyltin which comprises passing an electric current through an anode containing tin and an electrolyte containing equimolar proportions of sodium aluminum tetramethyl and sodium aluminum tetraethyl at a temperature of about 100 C. and a current density of 0.25 amperes per square centimeter.

2. A process for the manufacture of tetrahydrocarbon tin compounds, the hydrocarbon radicals thereof predominating in radicals of at least two carbon atoms, comprising passing an electric current through an electrolyte and a tin containing anode, said electrolyte consisting essentially of alkali metal aluminum tetrahydrocarbon, the hydrocarbon radicals in said electrolyte including from 5 to percent methyl groups.

3. A process for the manufacture of tetraalkyl tin comprising forming an electrolyte from an alkali metal aluminum tetramethyl and alkali metal aluminum tetraethyl, the alkali metal aluminum tetramethyl being in proportions of from about 5 to 95 mole percent, and charging to an electrolytic zone, and electrolyzing by passing an electric current therethrough and through a tin anode in contact therewith and'forming thereby tetraalkyl tin, wherein the alkyl groups thereof predominate in non-metal groups, and removing said tetraalkyl tin from the electrolysis zone.

4. The process of claim 3 wherein the alkali metals of the electrolyte compounds are different.

References Cited in the file of this patent UNITED STATES PATENTS 2,849,349 Ziegler et al. Aug. 26, 1958 FOREIGN PATENTS 214,834 Australia Apr. 24, 1958 

1. A PROCESS FOR THE MANUFACTURE OF TETRAETHYLTIN WHICH COMPRISES PASSING AN ELECTRIC CURRENT THROUGH AN ANODE CONTAINING TIN AND AN ELECTROLYTE CONTAINING EQUIMOLAR PORPORTIONS OF SODIUM ALUMINUM TETRAMETHYL AND SODIUM ALUMINUM TETRAETHYL AT A TEMPERATURE OF ABOUT 100*C. AND A CURRENT DENSITY OF 0.25 AMPERE PER SQUARE CENTIMETER. 